A variety of techniques and devices are commercially available for the detection and measurement of substances present in fluid or other translucent samples by determining the light absorbance of the sample. However, commercially available devices are limited in that they cannot suitably determine mid-UV absorbance of samples where the wavelength of the UV light is less than 300 nanometers. This limitation in commercial devices is due to the fact that commercial multi-assay plate devices do not have inexpensive mid-UV transparent multi-assay plates having well bottoms that will allow mid-UV light to pass vertically through the hole in the top of the multi-assay plate cylinders, through the sample, and thereafter pass unobstructed out through the well bottoms of the multi-assay plate mid on to the photodetector/detector board. Expensive UV-transparent multi-assay plates made of quartz are available but the cost is relatively great at about $1000 for a 96-well multi-assay plate made of quartz.
The present invention incorporates by reference the "Background of the Invention" for U.S. Pat. Nos. 4,968,148 and 5,112,134. As discussed in U.S. Pat. Nos. 4,968,148 and 5,112,134, the prior art has many problems and limitations. Although the vertical beam absorbance reader, taught in U.S. Pat. Nos. 4,968,148 and 5,112,134, solves or diminishes these problems and limitations, it has been discovered that mid-UV absorbance in multi-assay plates can be obscured because the inexpensive prior art devices made of polymeric materials devices are not designed for mid-UV light. Specifically, the prior devices have non-UV transparent multi-assay plates that prevent an accurate measurement of the UV absorbance of the sample under analysis. Mid-UV transparent multi-assay plates can be made of quartz but such devices are expensive and are not amenable to routine use.